This invention resides jointly in the fields of surgery and tissue culture and is particularly directed to an apparatus used for the expansion of animal tissue from an original, natural size to a larger size, usually with the intention of using the expanded tissue to replace defective tissue in the body of a living patient.
Tissue replacement is an essential component of reconstructive surgery after burns, trauma, tumor excision, and correction of congenital anomalies. For example, there are approximately 1 million bums per year in the U.S. alone, which result in about 100,000 admissions to burn units, about ⅓ of which require skin grafting.
The best possible skin available for grafting would be skin from the same patient taken from a donor site elsewhere on the body (referred to as an autograft). Suitable skin graft donor sites, however, are limited not only by body surface area, but can also be affected by previous graft harvest or trauma. There are times, when donor skin is limited and the amount of skin required for grafting is quite large, that sufficient autografts are not available. Because of the importance of the skin in preventing infection, either the donor skin must be used to cover a larger area than it originally covered or some suitable replacement material must be used. Harvesting of multiple skin grafts from the same donor site is often used, but such harvesting requires weeks to months between procedures for new skin to grow on the donor site. It is also a very traumatic technique, since multiple painful operations must be undertaken.
In a similar manner, other tissues also require replacement after traumatic injury, tumor excision, and other medical situations involving tissue loss. Autografts are preferred for muscle, cartilage, tendon, nerve, and other tissue replacement whenever possible in order to reduce host vs. graft immunity issues. Under appropriate circumstances, donor tissues derived from sources other than the recipient are acceptable for both skin and other tissues, but usually only as temporary replacements. For example, in patients suffering from large bums with limited donor skin sites, cadaver allografts are commonly used for temporary skin coverage, but ultimately such allografts are rejected and a permanent autograft is required. In addition, allografts also pose a risk of infection of the recipient by viruses or other disease-causing organisms present in the donor, such as infection by human immunodeficiency virus or hepatitis virus.
Artificial tissues have been developed in order to avoid the problems associated with allografts. For example, to aid in the grafting of skin on patients with limited donor areas, cultured epithelial cells derived from the patient being treated have been utilized in many grafting applications. In general, the cells are used in the form of a monolayer of epithelial cells grown on a culture medium. Preparation of such cultures requires many weeks or months, and the product is quite difficult to handle because of its fragility, even when multiple epidermal cell layers are used to form a multi-layer skin substitute.
Tissue expansion techniques, which were developed as in vivo techniques, have been used in plastic surgery for over a decade and can be helpful in increasing the area of donor tissue. Skin is not the only tissue that can be and has been expanded, although it is the most common. Other tissues have been expanded in surgical and other in vivo situations. Arteries, peripheral nerves, and skin have all been expanded in human clinical trials. Ureter, small bowel, and bladder have been expanded in animal trials.
The techniques used for in vivo tissue expansion are similar for all tissue types and involve mechanically stretching the tissue while the tissue is still attached to the patient""s body. For example, by placing an expander subcutaneously and injecting it with saline, skin can be expanded and its surface area increased. This allows reconstruction with local skin after expansion of an adjacent tissue bed.
Background information in the general field of tissue expansion, including techniques suitable for skin grafting and tissue replacement, is available in the patent and scientific literature. A number of exemplary patents and scientific publications are cited below, both as examples of existing technology and to provide additional basis and support for ancillary technology related to the practice of the present invention:
U.S. Pat. No. 5,882,353 entitled xe2x80x9cMechanical tissue expanderxe2x80x9d
U.S. Pat. No. 5,858,003 entitled xe2x80x9cSystems and methods for promoting tissue growthxe2x80x9d
U.S. Pat. No. 5,855,588 entitled xe2x80x9cCombination dissector and expanderxe2x80x9d
U.S. Pat. No. 5,788,627 entitled xe2x80x9cCavemosal extension implantsxe2x80x9d
U.S. Pat. No. 5,776,159 entitled xe2x80x9cCombination dissector and expanderxe2x80x9d
U.S. Pat. No. 5,630,843 entitled xe2x80x9cDouble chamber tissue expanderxe2x80x9d
U.S. Pat. No. 5,618,310 entitled xe2x80x9cTissue, expansion and approximation devicexe2x80x9d
U.S. Pat. No. 5,549,713 entitled xe2x80x9cMethod for skin tissue expansionxe2x80x9d
U.S. Pat. No. 5,507,775 entitled xe2x80x9cTissue expansion and approximation devicexe2x80x9d
U.S. Pat. No. 5,476,479 entitled xe2x80x9cHandle for endoscopic surgical instruments and jaw structurexe2x80x9d
U.S. Pat. No. 5,441,540 entitled xe2x80x9cMethod and apparatus for skin tissue expansionxe2x80x9d
U.S. Pat. No. 5,425,760 entitled xe2x80x9cTissue expander apparatus, and methods of constructing and utilizing samexe2x80x9d
U.S. Pat. No. 5,158,571 entitled xe2x80x9cTissue expander and method for expanding tissuexe2x80x9d
U.S. Pat. No. 5,092,348 entitled xe2x80x9cTextured tissue expanderxe2x80x9d
U.S. Pat. No. 5,005,591 entitled xe2x80x9cSelf-inflating tissue expanderxe2x80x9d
U.S. Pat. No. 4,904,267 entitled xe2x80x9cMethod and device for fixing a joint prosthesisxe2x80x9d
U.S. Pat. No. 4,863,469 entitled xe2x80x9cMethod and apparatus for expanding nerve tissuexe2x80x9d
U.S. Pat. No. 4,828,560 entitled xe2x80x9cSpring ring tissue expanderxe2x80x9d
U.S. Pat. No. 4,800,901 entitled xe2x80x9cBalloon-type Tissue expansion devicexe2x80x9d
U.S. Pat. No. 4,643,733 entitled xe2x80x9cPermanent reconstruction implant and method of performing human tissue expansionxe2x80x9d
U.S. Pat. No. 4,157,085 entitled xe2x80x9cSurgically implantable tissue expanding device and the method of its usexe2x80x9d
Argenta, xe2x80x9cControlled tissue expansion in reconstructive tissue,xe2x80x9d Brit. J. Plas. Surg., 37:520-529 (1984)
Argenta et al., xe2x80x9cThe Use of Tissue Expansion in Head and Neck Reconstruction,xe2x80x9d Ann. Plast. Surg., 11:31-37 (1983).
Arons et al., xe2x80x9cThe surgical applications and implications of cultured human epidermis: A comprehensive review,xe2x80x9d Surgery, 111:4-11 (1992)
Carney, xe2x80x9cGeneration of autograft; the state of the art,xe2x80x9d Burns, 12:231-235 (1986).
Chen, xe2x80x9cAn animal experiment on short gut lengthening,xe2x80x9d Chin. Med. J. (Engl.), 110:354-357 (1997).
Gallico, xe2x80x9cBiologic Skin Substitutes,xe2x80x9d Clinics in Plastic Surgery, 17:519-526 (1990)
Greenwald et al., xe2x80x9cFull-Thickness Skin Wound Explants in Tissue Cultures: A Mechanical Evaluation of Healing,xe2x80x9d Plastic and Reconstructive Surgery, 90:289-294 (1992)
Kirsner et al, xe2x80x9cThe Biology of Skin Grafts,xe2x80x9d Arch. Dermatol., 129:481-483 (1993)
Liatsikos et al, xe2x80x9cTissue expansion: a promising trend for reconstruction in urology,xe2x80x9d J. Endourol., 14:93-96 (2000).
Nanchahal and Ward, xe2x80x9cNew grafts for old? A review of alternatives to autologous skin,xe2x80x9d Brit. J. Plas. Surg., 45:354-363 (1992)
Satar and Atala, xe2x80x9cProgressive dilation for bladder tissue expansion,xe2x80x9d J. Urol., 162:829-831 (1999).
Stifelman and Hensle, xe2x80x9cUreteral tissue expansion for bladder augmentation: a long term prospective controlled trial in a porcine model, xe2x80x9d J. Urol., 160:1826-1829 (1998).
Sung Shin Wee et al., xe2x80x9cContinuous versus intraoperational expansion in the pig model,xe2x80x9d Plastic and Reconstructive Surgery, 90:808-814 (1992)
A particularly useful advance in the field of tissue expansion was initiated by Dr. Joshua Korman, who developed the first process for in vitro skin expansion in the 1990s. The investigations of Dr. Korman resulted in the issuance of two U.S. patents, U.S. Pat. No. 5,686,303, entitled xe2x80x9cMethod of Growing Vertebrate Skin In Vitro,xe2x80x9d and U.S. Pat. No. 5,914,264, entitled xe2x80x9cApparatus for Growing Vertebrate Skin In Vitro.xe2x80x9d The method involves growing complete vertebrate skin in vitro by obtaining a segment of vertebrate skin, positioning the skin segment in an artificial cell-growth medium containing sufficient nutrients to maintain growth of cells of the skin, and subjecting the skin segment to stretching forces while the skin segment is in the medium. Skin produced by the method and an apparatus for carrying out the method were also disclosed in these patents.
Even this improvement, which eliminates much of the pain and discomfort associated with in vivo skin expansion, can itself be improved by increasing the rate of tissue expansion in order to improve the life of the patient who is waiting for tissue expansion to be completed so that a defective tissue can be replaced with the expanded tissue.
In the past, investigations in tissue expansion have demonstrated that use of continuous expansion forces in post operative situations over a period of three days or more is superior to intraoperative tissue expansion, even when the intraoperative procedure involved three three-minute cycles of pressure increase and decrease (i.e., a manual procedure performed by the surgeon during surgery). See, Sung Shin Wee et al, xe2x80x9cContinuous versus intraoperative expansion in the pig model,xe2x80x9d Plastic and Reconstructive Surgery, 90:5, 808-814 (1992). Although xe2x80x9ccycling of pressurexe2x80x9d is mentioned (along with other factors; p.811) in a section discussing potential additional skin expansion, there is no indication that the rate of expansion would be increased by such cycling. Instead, there is simply an indication that the total volume of expansion did not plateau in the study, so that a greater total volume might be obtained by various techniques.
Accordingly, it remains desirable to develop an apparatus that will improve the rate of tissue expansion. Investigations on rate improvement have continued in the laboratory founded by Dr. Korman, and results of those investigations are the subject of the present patent application.